Turbulence evolution and its characteristics of gas–liquid two-phase flow in 90° branched pipelines

Ninety-degree branch pipes are widely used in oil and gas transportation networks. This study systematically investigates gas–liquid two-phase flow in 90° confluence sections using integrated experimental and numerical approaches. Three branch configurations (horizontal and vertical), two diameter ratios (0.4 and 0.25), inlet velocities (0.1, 0.2, and 0.3 m/s), and gas volume fractions (5%, 10%, and 20%) are examined. Computational fluid dynamics simulations employ the volume of fluid model coupled with the shear stress transport k–ω turbulence model, while experiments use pressure transducers and signal processing techniques. The results show that branch orientation does not significantly alter laminar formation but affects vortex diffusion pre- and post-confluence. Reducing the diameter ratio from 0.4 to 0.25 quantitatively enhances local turbulence intensity: fluid kinetic energy increases by 45% at the branch inlet and 37% at the confluence, while the pressure drop rises by up to 35%. When the inlet velocity increases from 0.1 to 0.3 m/s, the confluence pressure drop increases by approximately 70%. A gas volume fraction exceeding 10% intensifies recirculation in the vertical branch, whereas an inlet velocity above 0.3 m/s suppresses it. Dual-branch pipes exhibit a turbulence intensity 44% higher than single-branch pipes under identical conditions. Higher gas volume fractions (e.g., 20% vs 10%) enhance turbulence intensity and flow stability but increase pressure drop fluctuations, and these quantitative findings elucidate the coupled effects of diameter ratio and gas content on vortex diffusion, turbulence enhancement, and pressure pulsation in 90° branch pipes, advancing the understanding of flow evolution in small-diameter-ratio branch pipes.